This invention relates to novel multiple gas discharge display/memory panels or units which have an electrical memory and which are capable of producing a visual display or representation of data such as numerals, letters, television display, radar displays, binary words, etc.
Multiple gas discharge display and/or memory panels of one particular type with which the present invention is concerned are characterized by an ionizable gaseous medium, usually a mixture of at least two gases at an appropriate gas pressure, in a thin gas chamber or space between a pair of opposed dielectric charge storage members which are backed by conductor (electrode) members, the conductor members backing each dielectric member typically being transversely oriented to define a plurality of discrete discharge volumes and constituting a discharge unit.
In some prior art panels the discharge units are additionally defined by surrounding or confining physical structure such as by cells or apertures in perforated glass plates and the like so as to be physically isolated relative to other units. In either case, with or without the confining physical structure, charges (electrons, ions) produced upon ionization of the gas of a selected discharge unit, when proper alternating operating potentials are applied to selected conductors thereof, are collected upon the surfaces of the dielectric at specifically defined locations and constitute an electrical field opposing the electrical field which created them so as to terminate the discharge for the remainder of the half cycle and aid in the initiation of a discharge on a succeeding opposite half cycle of applied voltage, such charges as are stored constituting an electrical memory.
Thus, the dielectric layers prevent the passage of substantial conductive current from the conductor members to the gaseous medium and also serve as collecting surfaces for ionized gaseous medium charges (electrons, ions) during the alternate half cycles of the A.C. operating potentials, such charges collecting first on one elemental or discrete surface area and then on an opposing elemental or discrete dielectric surface area on alternate half cycles to constitute an electrical memory.
An example of a panel structure containing non-physically isolated or open discharge units is disclosed in U.S. Pat. No. 3,499,167 issued to Theodore C. Baker et al.
An example of a panel containing physically isolated units is disclosed in the article by D. L. Bitzer and H. G. Slottow entitled "The Plasma Display Panel -- A Digitally Addressable Display With Inherent Memory, " Proceeding of the Fall Joint Computer Conference, IEEE, San Francisco, California, Nov. 1966, pages 541-547. Also reference is made to U.S. Pat. No. 3,559,190.
In the operation of the panel, a continuous volume of ionizable gas is confined between a pair of dielectric surfaces backed by conductor arrays forming matrix elements. The cross conductor arrays may be orthogonally related (but any other configuration of conductor arrays may be used) to define a plurality of opposed pairs of charge storage areas on the surfaces of the dielectric bounding or confining the gas. Thus, for a conductor matrix having H rows and C columns the number of elemental discharge volumes will be the product H .times. C and the number of elemental or discrete areas will be twice the number of elemental discharge volumes.
In addition, the panel may comprise a so-called monolithic structure in which the conductor arrays are created on a single substrate and wherein two or more arrays are separated from each other and from the gaseous medium by at least one insulating member. In such a device the gas discharge takes place not between two opposing members, but between two contiguous or adjacent members on the same substrate.
It is also feasible to have a gas discharge device wherein some of the conductive or electrode members are in direct contact with the gaseous medium and the remaining electrode members are appropriately insulated from such gas.
In addition to the matrix configuration, the conductor arrays may be shaped otherwise. Accordingly, while the preferred conductor arrangement is of the crossed grid type as shown herein, it is likewise apparent that where a maximal variety of two dimensional display patterns is not necessary, as where specific standardized visual shapes (e.g., numerals, letters, words, etc.) are to be formed and image resolution is not critical, the conductors may be shaped accordingly.
The gas is one which produces visible light or invisible radiation which stimulates a phosphor (if visual display is an objective) and a copious supply of charges (ions and electrons) during discharge. In an open cell Baker et al type panel, the gas pressure and the electric field are sufficient to laterally confine charges generated on discharge within elemental or discrete dielectric areas within the perimeter of such areas, especially in a panel containing non-isolated units.
In the prior art, a wide variety of gases and gas mixtures have been utilized as the gaseous medium in gas discharge devices, especially of the direct current type. Typical of such gases include CO; CO.sub.2 ; halogens; nitrogen; NH.sub.3 ; oxygen; water vapor; hydrogen; hydrocarbons; P.sub.2 O.sub.5 ; boron fluoride; acid fumes; TiCl.sub.4 ; Group VIII gases; air; H.sub.2 O.sub.2 ; vapors of sodium, mercury, thallium, cadmium, rubidium, and cesium; carbon disulfide; laughing gas; H.sub.2 S; deoxygenated air; phosphorus vapors; C.sub.2 H.sub.2 ; CH.sub.4 ; naphthalene vapor; enthracene; freon; ethyl alcohol; methylene bromide; heavy hydrogen; electron attaching gases; electron free gases; sulfur hexafluoride; tritium; radio active gases; and the rare or inert gases.
In one particular practice of this invention, outstanding results have been obtained using at least one, typically two or more, rare gases, especially mixtures of neon, xenon, krypton, and argon. In addition, beneficial amounts of other components may be present such as helium and/or mercury.
As described in the Baker et al patent, the space between the dielectric surfaces occupied by the gas is such as to permit photons generated on discharge in a selected discrete or elemental volume of gas to pass freely through the gas space and strike surface areas of dielectric remote from the selected discrete volumes, such remote, photon struck dielectric surface areas thereby emitting electrons so as to condition at least one elemental volume other than the elemental volume in which the photons originate.
With respect to the memory function of a given discharge panel, the allowable distance or spacing between the dielectric surfaces depends, inter alia, on the frequency of the alternating current supply, the distance typically being greater for lower frequencies.
While the prior art does disclose gaseous discharge devices having externally positioned electrodes for initiating a gaseous discharge, sometimes called "electrodeless discharge, " such prior art devices utilized frequencies and spacings or discharge volumes and operating pressures such that although discharges are initiated in the gaseous medium, such discharges are ineffective or not utilized for charge generation and storage at higher frequencies; although charge storage may be realized at lower frequencies, such charge storage has not been utilized in a display/memory device in the manner of the Bitzer-Slottow or Baker et al invention.
The term "memory margin" is defined herein as EQU M.M. = (V.sub.f - V.sub.E)/(V.sub.f /2)
where V.sub.f is the half amplitude of the smallest sustaining voltage signal which results in a discharge every half cycle, but at which the cell is not Bi-stable and V.sub.E is the half amplitude of the minimum applied voltage sufficient to sustain discharges once initiated.
It will be understood that the basic electrical phenomenon utilized in this invention is the generation of charges (ions and electrons) alternately storable at pairs of opposed or facing discrete points or areas on a pair of dielectric surfaces backed by conductors connected to a source of operating potential. Such stored charges result in an electrical field opposing the field produced by the applied potential that created them and hence operate to terminate ionization in the elemental gas volume between opposed or facing discrete points or areas of dielectric surface. The term "sustain a discharge" means producing a sequence of momentary discharges, one discharge for each half cycle of applied alternating sustaining voltage, once the elemental gas volume has been fired, to maintain alternate storing of charges at pairs of opposed discrete areas on the dielectric surfaces.
In accordance with the practice of this invention, the operating characteristics of a gaseous discharge display/memory panel are enhanced and improved by applying to at least one dielectric surface a beneficial amount of at least one inorganic aluminum compound selected from non-aluminum oxides.
The inorganic oxide compound is applied to the dielectric surface as a continuous or discontinuous layer.
As used herein, the term "layer" is intended to be all inclusive of other similar terms such as film, deposit, coating, finish, spread, covering, etc.
The inorganic aluminum compound is applied to the dielectric surface (or over a previously applied dielectric layer) by any convenient means including not by way of limitation vapor deposition; vacuum deposition; chemical vapor deposition; wet spraying upon the surface a mixture or solution of the layer substance suspended or dissolved in a liquid followed by evaporation of the liquid; dry spraying of the layer upon the surface; thermal evaporation using direct heat, electron beam, or laser; plasma flame and/or arc spraying and/or deposition; and sputtering target techniques.
In one embodiment hereof, a layer of the inorganic aluminum compound is applied to the dielectric surface, such as by one of the foregoing methods, especially electron beam evaporation.
Although the inorganic aluminum compound is typically applied on the charge storage side of the dielectric member, it is contemplated that such compound may be applied to a non-charge storage side, such as on the electrode array side of a dielectric.
The selected inorganic compound is typically a non or semi-conductor. However, conductor compounds may be used if the material is appropriately isolated (such as covering with an over layer) so as not to be in electrical contact with a source of potential and/or ground. Likewise, if a conductor material is used in a multiple cell device, the geometric arrangement of the material may be such that no two cells are electrically connected by the conductive material. For example, the selected aluminum compound could be deposited as a spot over each discharge site.
Typical inorganic aluminum non-oxide compounds include aluminum orthoarsenate, aluminum fluosilicate, aluminum nitride, aluminum metal phosphate, aluminum orthophosphate, aluminum selenide, aluminum silicate, aluminum sulfate, aluminum sulfide, and aluminum thallium sulfate.
One or more layers of other substances may be used in combination with the inorganic compounds of this invention, especially compounds of lead, titanium, silicon, zirconium, hafnium, Group I A (especially cesium), Group II A, rare earths (especially thorium), and phosphor materials. Typically such substances will be oxides. Such layers may be applied to the dielectric before and/or after the layer of this invention.
Each layer, including the layer of this invention, is applied to the dielectric, as a surface or sub-layer, in an amount sufficient to obtain the desired beneficial result, usually to a thickness of at least about 100 angstrom units with a range of about 200 angstrom units per layer up to about 1 micron (10,000 angstrom units) per layer.
In the fabrication of a gaseous discharge panel, the dielectric material is typically applied to and cured on the surface of a supporting glass substrate or base to which the electrode or conductor elements have been previously applied. The glass substrate may be of any suitable composition such as a soda lime glass composition. Two glass substrates containing electrodes and cured dielectric are then appropriately sealed together, e.g. using thermal means, so as to form a panel.
In one preferred practice of this invention, the aluminum compound layer, and any other layer, is applied to the surface of the cured dielectric before the panel heat sealing cycle, with the substrate temperature during application ranging from about 150.degree. F. to about 600.degree. F.
The use of the aluminum compound layer in accordance with this invention has many potential beneficial results, especially the providing of stable panel operating voltages which do not significantly change with panel operating time.